Heretofore, glow discharge decomposers used for the production of solar cells and the like have been mostly employed in the form of an apparatus based on a parallel-plate method shown in FIG. 4. The parallel-plate method is suitable for the formation of films of large area but has a disadvantage in that an electric discharge taking place between an RF electrode 6 and an opposite electrode 7 results in the plasma damaging of a thin film formed on a substrate 3 placed on the RF electrode or the opposite electrode (ground electrode). Moreover, since an electric discharge also takes place on the back of the RF electrode 6 forming the RF electrode pair, it is necessary to provide a shield for suppressing this discharge. However, the provision of such a shield has the disadvantage of making the discharge unstable.
Hamakawa et al. proposed a transverse plasma method (Japanese Examined Patent Publication (Tokkyo Kokoku) No. 42126/1983), as shown in FIG. 5, to minimize damage caused by plasma to thin films formed. However, there is naturally a limit to the distance between the RF electrode 6 and the ground electrode 7, and hence to the size of the substrate 3 to be used, which results in a disadvantage that it is impossible to obtain a thin film of large area. Moreover, in order to avoid deposition of a thin film on the electrode pair, a container such as one designated by the numeral 4 is required.
In view of the actual circumstances described above, the present inventors have conducted intensive research to minimize damage caused by plasma to a thin film formed on the substrate in the parallel-plate method and to dispense with the shield required on the back of the RF electrode and the container used in the transverse plasma method while forming a thin film of large area, and have found out that the object can be attained by the present invention, and then have completed the present invention.